Field of the Invention
The present invention relates generally to a method and apparatus for reducing the strength of pulsating magnetic fields generated by various electronic devices.
Recently, it has been discovered that pulsating magnetic fields as well as varying electromagnetic fields affect biological matter and, consequently, cause health problems in human and animals, ranging from miscarriages to cancer. These discoveries have been made under laboratory conditions and through epidemiological studies.
Pulsating magnetic fields are very prevalent in modern society. Many of the electric devices man contacts in daily life emit pulsating magnetic fields. In television (TV) sets, video display terminals (VDT), personal computer monitors (PCM), etc., the pulsating magnetic field is produced by the deflecting magnetic coils which control the electron beam forming the display. The induced electric fields produced by the pulsating magnetic field associated with the deflecting magneticcoils in VDT, PCM, and TV sets expose human beings to prolonged action of extremely low frequency (ELF)and very low frequency (VLF) induced electric fields. Unreduced by shielding means these fields are generally greater than 1 milligauss.
In addition, biological effects may be induced by low frequency pulsating magnetic fields generated by high power lines and substation transformers. Electrical appliances, spark plugs in cars and trucks and electric devices used in home and offices also produce pulsating magnetic fields with strengths greater than 1 milligaus (mG). Among these are electric razors, fluorescent light transformers, electric clocks, hair dryers, electric heaters, microwave ovens, personal radio transmitters, and electric blankets. In fact, it has been published that there is a significant correlation between electric blankets and miscarriages. Even in hospitals operating rooms, due to the high-tech electronic instrumentation, hazardous electromagnetic fields have been detected.
Presently,there are no uniform standard for minimum magnetic field exposure. Epidemiological studies suggest that ELF values over 2-3 mG are hazardous for the health of humans under continuous exposure to these pulsating magnetic fields. At least one national authority in the biological effects of electromagnetic fields recommends a maximum exposure value of 0.3 mG. An advisory board to the Swedish government suggests a maximum VLF value of 0.25 mG for magnetic induction as measured at 20 inches from the screen of VDTs, PCMs, and TV sets.
There are several collections of experimental results and theoretical discussions of the effects of electromagnetic fields. Of interest is Handbook of Biological Effects of Electromagnetic Fields, Ed. C. Polk and E. Postow, CRC Press, Inc., Boca Raton Fla., 1988, Part II, Chapters 2, 3 and 5, in which biological effects are considered in relation to the action of ELF electromagnetic fields. In the group of epidemiological related to ELF fields, the paper by N. Wertheimer and E. Leeper, American Journal of Epidemiology, vol. 109, 273 (1979), is very illustrative about the relationship between exposure to 60 Hz magnetic fields from electric lines and childhood cancer. Another paper by J. Phillips et al., International Radiation Biology, 49, 463, (1986), shows that 60 Hz magnetic and electromagnetic fields increase the rate of growth of human cancer cells. Also, R. O. Becker, M.D., in Cross Currents: The Promise of Electromedicine--The Perils of Electropollution, Jeremy P. Tarcher, Inc., Los Angeles, Calif., 1990, p. 270, comments that studies "indicate that residential exposure to ambient fields greater than 3 milligauss are significantly related to increases in the incidence of childhood cancer. There is good evidence that such fields may also be associated with adult cancers. In risk protection, a factor of ten is generally applied. In this case, that would drop the theoretical safe level to 0.3 milligauss." Becker says: "Because of practical considerations, I advocate a maximum strength of 1 milligauss for continuous exposure to 60 Hz fields. Finally the paper by J. C. Cure', Cancer: An Electrical Phenomenon, Part 1 of 3, published in Health Consciousness, vol. XII, no. 5, p. 83, Oct. 1991, shows the electrophysical basis of the action of electromagnetic fields at a cellular level.
As it is well known the magnetic permeability of an immense variety of materials, including biological matter, is practically equal to the magnetic permeability of vacuum. This fact implies that permanent and pulsating magnetic fields penetrate and go through practically every kind of substances with the exception of ferromagnetic materials. Thus, to block magnetic fields with material shields is not practical unless one is willing to use enclosures made out of expensive ferromagnetic materials. Accordingly, magnetic field exposure represents a serious health problem that demands prompt solutions. U.S. Pat. No. 4,634,930 to Toshiyasu discloses a device which comprises a coil placed internal to a cathode ray tube display device for the purpose of cancelling electromagnetic field noise generated by the deflection yokes of the cathode ray tube.
U.S. Pat. No. 4,931,625 to Marlinski, discloses a device for shielding electromagnetic radiation. The device includes a cover arranged to enclose the heating means so as to block and contain the electromagnetic radiation emitted from heating pads and other similar devices. The cover has a layer of electrically conductive material and a ground connection for electrically grounding the conductive layer.
U.S. Pat. No. 4,891,468 to Andrae discloses a device to shield against electromagnetic fields. This invention relates to a device consisting of a shielding film of metal, in particular aluminum or metalized plastic, to shield against an electromagnetic field.
U.S. Pat. No. 4,992,624 to Benson et al., discloses a magnetic shield for visual display terminals. The invention is designed to shield the pulsating magnetic field created by the flyback transformer of a cathode ray tube display terminal. The magnetic shield consists of a layer of metal conductor, for example mu metal (magnalloy), and a layer of insulator (like polyester film), placed on top of the metal layer. The double layer is rolled to adopt the shape of a cylinder, which is installed around the flyback transformer.
U.S. Pat. No. 5,107,179 to Vidovich discloses a stray electromagnetic field reducing device comprising a pair of closed wire loops placed inside a cathode ray tube device and in physical contact with the cathode ray tube. One loop includes a capacitive element to cause the loop to form a resonant circuit. The resonant circuit allows greater induced current to flow in the loop with the consequence of improved cancellation of the stray cathode ray tube device generated fields.
Patents to Vidovich and to Toshiyasu, et. al. do not teach a device external to the cathode ray tube (CRT) enclosure, in fact, both patents disclose devices in physical contact with the CRT itself. Consequently, no disclosure to date has provided an external means of field cancellation for such devices as televisions and personal computers. Presently, there are approximately 100 million personal computers in the United States and many more world wide which were manufactured without benefit of the internal field cancellation devices disclosed by Vidovich and Toshiyasu et al. The present invention addresses a means for upgrade of these computers, and other devices using CRT's by simple placement of the present invention external to the computer or other CRT device.